ABSTRACTThe present study examined the changes in protein expression in Spirulina platensis upon exposure to high temperature, with the changes in expression analyzed at the subcellular level. In addition, the transcriptional expression level of some differentially expressed proteins, the expression pattern clustering, and the protein-protein interaction network were analyzed. The results obtained from differential expression analysis revealed up-regulation of proteins involved in two-component response systems, DNA damage and repair systems, molecular chaperones, known stress-related proteins, and proteins involved in other biological processes, such as capsule formation and unsaturated fatty acid biosynthesis. The clustering of all differentially expressed proteins in the three cellular compartments showed: (i) the majority of the proteins in all fractions were sustained tolerance proteins, suggesting the roles of these proteins in the tolerance to high temperature stress, (ii) the level of resistance proteins in the photosynthetic membrane was 2-fold higher than the level in two other fractions, correlating with the rapid inactivation of the photosynthetic system in response to high temperature. Subcellular communication among the three cellular compartments via protein-protein interactions was clearly shown by the PPI network analysis. Furthermore, this analysis also showed a connection between temperature stress and nitrogen and ammonia assimilation.

Figure 14: Predicted protein-protein interaction network based on differentially expressed proteins identified in this work, constructed by using the available data from Cyanobase and the Spirulina genome database. The networks show protein-protein interaction partners in the plasma membrane fraction. The symbols, ⌂ and its reversion, represent the up- and down-regulated proteins identified in this study, respectively. The letters A and B after spot numbers in the nodes represent the pH ranges of 3-10 and 4-7 in the first dimension of the 2D-DIGE, respectively.

Mentions:
Several differentially expressed proteins identified in this study can be mapped onto the PPI network available on Cyanobase (Fig. 14, 15 and 16). The potential PPIs shown in the three subcellular fractions represent interesting linkages or cross-talks among the three cellular compartments. For example, in the PM fraction, two component system sensory histidine kinase (spot#1564), ABC transporter (spot#2179), ferredoxin-glutamate synthase (spot#1388) and carboxypeptidase (spot#1284) show interactions with the photosynthetic system. In the soluble fraction, the phosphorylated form of multi-sensor signal transduction histidine kinase (spot#1883) interacts with several periplasmic proteins. However, in the TM fraction, the same protein was found in the non-phosphorylated form. The interactions found in the thylakoid membrane also show communication with the other two fractions.

Figure 14: Predicted protein-protein interaction network based on differentially expressed proteins identified in this work, constructed by using the available data from Cyanobase and the Spirulina genome database. The networks show protein-protein interaction partners in the plasma membrane fraction. The symbols, ⌂ and its reversion, represent the up- and down-regulated proteins identified in this study, respectively. The letters A and B after spot numbers in the nodes represent the pH ranges of 3-10 and 4-7 in the first dimension of the 2D-DIGE, respectively.

Mentions:
Several differentially expressed proteins identified in this study can be mapped onto the PPI network available on Cyanobase (Fig. 14, 15 and 16). The potential PPIs shown in the three subcellular fractions represent interesting linkages or cross-talks among the three cellular compartments. For example, in the PM fraction, two component system sensory histidine kinase (spot#1564), ABC transporter (spot#2179), ferredoxin-glutamate synthase (spot#1388) and carboxypeptidase (spot#1284) show interactions with the photosynthetic system. In the soluble fraction, the phosphorylated form of multi-sensor signal transduction histidine kinase (spot#1883) interacts with several periplasmic proteins. However, in the TM fraction, the same protein was found in the non-phosphorylated form. The interactions found in the thylakoid membrane also show communication with the other two fractions.

Bottom Line:
In addition, the transcriptional expression level of some differentially expressed proteins, the expression pattern clustering, and the protein-protein interaction network were analyzed.The results obtained from differential expression analysis revealed up-regulation of proteins involved in two-component response systems, DNA damage and repair systems, molecular chaperones, known stress-related proteins, and proteins involved in other biological processes, such as capsule formation and unsaturated fatty acid biosynthesis.Furthermore, this analysis also showed a connection between temperature stress and nitrogen and ammonia assimilation.

ABSTRACTThe present study examined the changes in protein expression in Spirulina platensis upon exposure to high temperature, with the changes in expression analyzed at the subcellular level. In addition, the transcriptional expression level of some differentially expressed proteins, the expression pattern clustering, and the protein-protein interaction network were analyzed. The results obtained from differential expression analysis revealed up-regulation of proteins involved in two-component response systems, DNA damage and repair systems, molecular chaperones, known stress-related proteins, and proteins involved in other biological processes, such as capsule formation and unsaturated fatty acid biosynthesis. The clustering of all differentially expressed proteins in the three cellular compartments showed: (i) the majority of the proteins in all fractions were sustained tolerance proteins, suggesting the roles of these proteins in the tolerance to high temperature stress, (ii) the level of resistance proteins in the photosynthetic membrane was 2-fold higher than the level in two other fractions, correlating with the rapid inactivation of the photosynthetic system in response to high temperature. Subcellular communication among the three cellular compartments via protein-protein interactions was clearly shown by the PPI network analysis. Furthermore, this analysis also showed a connection between temperature stress and nitrogen and ammonia assimilation.